Non-Newtonian flow effects on the coalescence and mixing of initially stationary droplets of shear-thinning fluids

Sun, Kai; Wang, Tianyou; Zhang, Peng; Law, Chung K.

doi:10.1103/physreve.91.023009

Cited by 20 publications

(23 citation statements)

References 32 publications

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“…They found that increasing the droplet viscosity suppresses the mixing and increasing the size disparity promotes the mixing. The internal mixing was also reported in several other numerical studies employing the volume of fluid (VOF) method [33][34][35] , the front-tracking method 31,32 and the lattice Boltzmann method [36][37][38] . Nevertheless, detailed investigation and physical interpretation of the mixing process have not been adequately addressed in these studies.…”

Section: Introductionsupporting

confidence: 52%

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

Xia

et al. 2017

Phys. Rev. Fluids

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This study employs an improved volume of fluid method and adaptive mesh refinement algorithm to numerically investigate the internal jet-like mixing upon the coalescence of two initially stationary droplets of unequal sizes. The emergence of the internal jet is attributed to the formation of a main vortex ring, as the jet-like structure shows a strong correlation with the main vortex ring inside the merged droplet. By tracking the evolution of the main vortex ring together with its circulation, we identified two mechanisms that are essential to the internal-jet formation: the vortex-ring growth and the vortex-ring detachment. Recognizing that the manifestation of the vortex-ring-induced jet physically relies on the competition between the convection and viscous dissipation of the vortex ring, we further developed and substantiated a vortex-ring-based Reynolds number ( = /4 ) criterion, where is the circulation of the detached main vortex ring and is the liquid kinematic viscosity, to interpret the occurrence of the internal jet at various Ohnesorge numbers and size ratios. For the merged droplet with apparent jet formation, the average mixing rate after jet formation increases monotonically with , which therefore serves as an approximate measure of the jet strength. In this respect, stronger internal jet is responsible for enhanced mixing of the merged droplet. _____________________________a) The first and second authors contributed equally to this work. b) Author to whom correspondence should be addressed. Electronic

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Section: Introductionsupporting

confidence: 52%

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

Xia

et al. 2017

Phys. Rev. Fluids

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“…Another important aspect of droplet coalescence is the subsequent internal mixing, which has gained increasing attentions in recent years for its relevance in the microfluidics and hypergolic propellant systems involving liquid-phase reactions [32][33][34][35][36][37][38] . An important understanding gained from the recent studies is that the internal mixing is minimal for the head-on collision of two identical droplets due to the intrinsic symmetry across the collision plane.…”

Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 99%

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Zhang

Yuan

et al. 2016

Combustion and Flame

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a b s t r a c tHypergolic ignition by the head-on collision of a smaller N,N,N ,N −tetramethylethylenediamine (TMEDA) droplet and a larger white fuming nitric acid (WFNA) droplet was experimentally investigated by using a droplet collision experimental apparatus equipped with a time-resolved shadowgraph, a photodetector and an infrared detector. The investigation was focused on understanding the influence of droplet collision and mixing, which vary with the collisional Weber number ( We = 20 −220) and the droplet size ratio ( = 1.2 −2.9) while have a fixed Ohnesorge number (Oh = 2.5 ×10 −3 ), on the hypergolic ignitability and the ignition delay times. The hypergolic ignition was found to critically rely on the heat release from of the liquid-phase reaction of TMEDA and nitric acid, which is subsequent to and enhanced by the effective mixing of the droplets of proper size ratios. Consequently, the ignitability regime nomogram in the We-space shows that the hypergolic ignition favors small s and large We s; the ignition delay times tend to decrease with either decreasing , or increasing We , or both. A non-monotonic variation of the ignition delay times with We was observed and attributed to the non-monotonic emergence of jet-like mixing patterns that enhance the droplet mixing and hence the liquid-phase reaction.

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“…We should state here that when performing such coalescence experiments, depending on the liquid viscosity, solubility and reactivity, it is possible to achieve partial or full mixing, or chemical reactions that evolve with different time scales. [42][43][44] Full image sequence is available in Movie M5.…”

Section:  mentioning

confidence: 99%

Contactless Transport and Mixing of Liquids on Self-Sustained Sublimating Coatings

et al. 2017

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Controlled handling of liquids and colloidal suspensions as they interact with surfaces, targeting a broad palette of related functionalities, is of great importance in science, technology, and nature. When small liquid volumes (drops on the order of microliters or nanoliters) need to be processed in microfluidic devices, contamination on the solid/liquid interface and loss of liquid due to adhesion on the transport channels are two very common problems that can significantly alter the process outcome, for example, the chemical reaction efficiency or the purity and the final concentration of a suspension. It is, therefore, no surprise that both levitation and minimal contact transport methods-including nonwetting surfaces-have been developed to minimize the interactions between liquids and surfaces. Here, we demonstrate contactless surface levitation and transport of liquid drops, realized by harnessing and sustaining the natural sublimation of a solid-carbon-dioxide-coated substrate to generate a continuous supporting vapor layer. The capability and limitations of this technique in handling liquids of extreme surface tension and kinematic viscosity values are investigated both experimentally and theoretically. The sublimating coating is capable of repelling many viscous and low-surface-tension liquids, colloidal suspensions, and non-Newtonian fluids as well, displaying outstanding omniphobic properties. Finally, we demonstrate how sublimation can be used for liquid transport, mixing, and drop coalescence, with a sublimating layer coated on an underlying substrate with prefabricated channels, conferring omniphobicity using a simple physical approach (i.e., phase change) rather than a chemical one. The independence of the surface levitation principle from material properties, such as electromagnetic, thermal or optical, surface energy, adhesion, or mechanical properties, renders this method attractive for a wide range of potential applications.

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Non-Newtonian flow effects on the coalescence and mixing of initially stationary droplets of shear-thinning fluids

Cited by 20 publications

References 32 publications

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Contactless Transport and Mixing of Liquids on Self-Sustained Sublimating Coatings

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